1. Field of the Invention
The present invention relates to a method of preparing complex-azo pigments and to complex-azo pigments both limited by (i.e., made by) the described process and not so limited (i.e., not so made) by the described process.
2. Discussion of the Background
Conventionally, azo pigments are available as organic electrophotographic photoreceptors, particularly useful as a charge generating material. Multilayer electrophotographic photoreceptor is one example of photoconductors includes an electroconductive support, a charge generating layer includes a charge generating material that generates a charge by means of light, and a charge transporting layer includes a charge transporting material that transports a charge injected from the charge generating layer.
A variety of azo compounds for use in the photoconductor are conventionally proposed, for example, benzidine bisazo compounds in unexamined published Japanese patent application No. (hereinafter referred to as JOP) 47-37543 and JOP 52-55643, stilbene bisazo compounds in JOP 52-8832, diphenyl hexatriene bisazo compounds in JOP 58-222152, and diphenyl butadiene bisazo compounds in JOP 58-222153. When only single azo pigment is used as a charge generating material in a photoreceptor has a sensitivity to narrow wavelength range and electrophotograph properties are changeable depending on environment. Therefore, a photoreceptor having single azo pigment doesn't have a demanded high-resolution property, and also it doesn't have sufficient properties for a high-speed copying machine or laser beam printer.
For solving these problems, a technology of mixing at least two pigments and using as generating materials is produced. For example, a method of mixing and having a phthalocyanine and a fluorenone azo pigment in Japanese patent No. 3326706 and JOP 2001-290296, a method of mixing and having a phthalocyanine and an azo pigment in JOP 9-127711, a method of mixing and having a metallophthalocyanine and a perylene pigment in JOP 2002-23399, a method of mixing and having a quinacridone pigment and a titanylphthalocyanine pigment in JOP 2007-334099, a method of mixing and having a titanylphthalocyanine pigment and other phthalocyanine pigment in JOP 3-9962. Even though pigments were developed as mentioned above, pigments for a photoconductor suitable for a high-speed copying machine having good quality of image forming have not been provided.
Pigments disclosed in documents mentioned above usually have poor solubility to organic solvents, so a method for purification of pigment is limited to a washing method using organic solvents. By the washing process, impurities in pigment can be remained after purification. As a method of mixing pigments, mechanical mixing, for example milling is used. In such a manner, mixing and making complex of pigments is difficult, so enough function as an organic photoconductor can't be provided. The method using acid pasting is disclosed, but for the method, it's necessary to use concentrated sulfuric acid, so an application of the method to producing pigments is limited because of problem in productivity.
From such situation, complex-azo pigments as a charge generating material that overcome conventional weak points are expected. A soluble precursor for pigments are disclosed in PCT patent application publications No. 2001-513119 (WO98/32802), but developing functions by making a pigment as a complex is not known.
Because of these reasons, a need exists for a charge generating material photoconductor suitable for a high-speed copying machine.